The use of superabsorbent polymer particles, especially in absorbent articles, is well known in the art. The superabsorbent polymer particles are typically made by grinding or otherwise shredding relatively large blocks of superabsorbent polymer. However, the size of the particles obtained by such grinding or shredding cannot be fully controlled. The obtained superabsorbent polymer particles hence typically have a certain particle size distribution and thus, there are particles of relatively large size (e.g. 1000 μm or even larger) while others are considerably smaller, such as less than 100 μm or even significantly smaller, with the majority of the particle sizes ranging in between. Small particles are often referred to as “fines”.
It is known that in order to have absorbent articles comprising superabsorbent polymer particles which exhibit good absorbing and containing functions, specific technical requirements need to be fulfilled by the superabsorbent polymer particles.
The superabsorbent polymer particles need first to be able to absorb the liquid exudates fast. The absorption speed of superabsorbent polymer particles has generally been characterized in the prior art by measuring the Free Swell Rate (FSR) of the particles.
In addition to having a high absorption speed, the superabsorbent polymer particles present in the absorbent core comprised by absorbent articles also need to be highly permeable to liquid. The permeability of the superabsorbent polymer particles has typically been characterized in the prior art by measuring the UPM (Urine permeability measurement) of the particles.
A poor permeability of the superabsorbent polymer particles may induce leakage of the absorbent article due to gel blocking. Gel blocking can occur in the absorbent core when swelling superabsorbent polymer particles block the void spaces between the particles. In such a case, the liquid exudates cannot or only slowly reach underneath layers of superabsorbent polymer particles disposed in the absorbent core. The liquid exudates remain on the surface of the absorbent core and may therefore leak from the absorbent article.
To address the problem of gel blocking, superabsorbent polymer particles are typically subjected to surface cross-linking, thus increasing the particle's stiffness and resistance to deformation upon swelling.
While surface cross-linking helps to increase the permeability of the superabsorbent polymer particles, the increase in permeability typically comes at the price of reduced capacity: Given the particles have a stiffer surface, they cannot swell as unhindered as non surface-cross-linked particles. This trade off is more pronounced for smaller superabsorbent polymer particles.
One way of reducing the number of fine particles without having to discard them is to form agglomerates of superabsorbent polymer particles.
The patent application US2010/0234531 of Evonik Stockhausen GmbH discloses a process for producing agglomerated superabsorbent polymer particles.
The patent application WO2015/175620 discloses agglomerated superabsorbent polymer particles which have been agglomerated by using a multivalent salt having a valence of three or higher.
Though several approaches to form agglomerated superabsorbent polymer particles have been described, there is still a need for an improved method of making agglomerated superabsorbent polymer particles as well as a need for improved agglomerated superabsorbent polymer particles.